The present proposal is a collaborative case-control study of a small cohort of patients diagnosed as having, on the basis of carefully established clinical criteria, presenile or senile dementia of the Alzheimer's type. Information will be obtained regarding factors possibly related to the development of this illness from these patients and from matched control subjects by means of a structured epidemiologic interview, by analyses of serum and cerebrospinal fluid for viral antibodies and for increased concentrations of aluminum and other metallic ions and by detailed family history searching for evidence of genetic defects. The natural history of the disorder and the correlation between the progressive mental changes, the electroencephalographic abnormalities and the changes in computer tomography of the brain will also be studied.